Why is this variable in equation 2 of the SQAIR paper a random vector of $n$ ones followed by a zero?
From my understanding of the paper, $Z^{pres}$ keeps track of the objects in the scene. For every step of the sequential inference, $z^{pres,i}$ takes either a 0 or a 1. A 1 represents that an object is present and it has to be explained by the remaining latent variables. 0 indicates that all the objects have been explained and inference is complete.